This project focuses on the mechanism of reactions of systems requiring adenosyl-cobalamin (coenzyme B12) specifically propanediol dehydratase. Experiments of three kinds are being carried out (1) kinetic and product studies using substrate analogues, such as glycerol, including observation of kinetic isotope effects and stereochemistry of specifically deuterated deriatives (2) esr experimentation of reacting systems for detection and characterization of possible radical-type intermediates and (3) attempts to isolate cobalamin-substrate or enzyme-substrate intermediates. Catalytic studies of serine proteases are aimed at observation and characterization of the tetrahedral intermediate with particular emphasis on the ionization behavior of the residues of the catalytic triad (asp-his-ser) and the role of charge transfer as the basis of the catalytic mechanism.